src/liblzma/check/crc64_small.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       crc64_small.c
   4 /// \brief      CRC64 calculation (size-optimized)
   5 //
   6 //  Author:     Lasse Collin
   7 //
   8 //  This file has been put into the public domain.
   9 //  You can do whatever you want with this file.
  10 //
  11 ///////////////////////////////////////////////////////////////////////////////
  12
  13 #include "check.h"
  14
  15
  16 static uint64_t crc64_table[256];
  17
  18
  19 #ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
  20 __attribute__((__constructor__))
  21 #endif
  22 static void
  23 crc64_init(void)
  24 {
  25         static const uint64_t poly64 = UINT64_C(0xC96C5795D7870F42);
  26
  27         for (size_t b = 0; b < 256; ++b) {
  28                 uint64_t r = b;
  29                 for (size_t i = 0; i < 8; ++i) {
  30                         if (r & 1)
  31                                 r = (r >> 1) ^ poly64;
  32                         else
  33                                 r >>= 1;
  34                 }
  35
  36                 crc64_table[b] = r;
  37         }
  38
  39         return;
  40 }
  41
  42
  43 extern LZMA_API(uint64_t)
  44 lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
  45 {
  46 #ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
  47         mythread_once(crc64_init);
  48 #endif
  49
  50         crc = ~crc;
  51
  52         while (size != 0) {
  53                 crc = crc64_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
  54                 --size;
  55         }
  56
  57         return ~crc;
  58 }